Takeshi Miki

Niobium Oxide Electrochromic Thin Films Prepared by Reactive DC Magnetron Sputtering

Nickel oxide electrochromic thin films were prepared by reactive DC magnetron sputtering. The as-deposited optical property and electrochromic behavior strongly depended on the target operation mode and the substrate temperature. The sample sputtered with low oxygen flow rate, high power and substrate temperature of 200-300° C showed a wide transmittance modulation range, and the deposition rate was as high as 30 nm/min. Its integrated luminous transmittance could be controlled from 6.6 to 82.3%. X-ray diffraction measurements of this sample in a colored state and bleached state suggested that the boundary and surface of NiO microcrystallites played an important role in the electrochromic reaction of sputtered nickel oxide films.

Ferroelectric properties of alkoxy-derived CaBi4Ti4O15 thin films on Pt-passivated Si

CaBi4Ti4O15 (CBTi144) thin films were prepared by spin coating a precursor solution of metal alkoxides. As-deposited thin films began crystallization below 550u200a°C and reached full crystallinity of a single phase of layered perovskite at 650u200a°C via rapid thermal annealing in oxygen. The 650u200a°C annealed CBTi144 thin film showed random orientation on Pt-passivated Si substrate and exhibited P-E hysteresis loops. The remanent polarization (Pr) and coercive electric field (Ec) were 9.4u200aμC/cm2 and 106 kV/cm, respectively, at 11 V. The dielectric constant and loss factor were 300 and 0.033, respectively, at 100 kHz.

Characterization of niobium oxide electrochromic thin films prepared by reactive d.c. magnetron sputtering

Abstract Niobium oxide electrochromic thin films were prepared by reactive d.c. magnetron sputtering, and their physical properties, such as surface structure, composition, optical transmittance, reflectance and absorption, were studied. The surface morphology of the heated sample is very different from that of the unheated sample. Auger electron spectroscopy (AES) measurements show that the composition of the amorphous film is close to Nb2O5 as well as the crystallized sample. The crystallized and amorphous samples show very different absorption behavior. The band gap is estimated to be 3.41 eV for the crystallized sample and 3.45 eV for the amorphous sample.

Microstructure Control and Dielectric/Piezoelectric Properties of Alkoxy-Derived Ba(Ti,Zr)O3 Thin Films

Lead-free ferroelectric Ba(Ti1-xZrx)O3 (BTZ, x=0.00–0.50) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by the chemical solution deposition (CSD) process using complex alkoxide solutions. When the Zr content x was increased, the crystallinity of BTZ thin films was changed from the typical random orientation to the (111) preferred orientation. From the composition dependence of the dielectric constant er and piezoelectric constant d33, the pinching region at room temperature of BTZ thin films consisting of nano-crystals appeared around x=0.20. For the BTZ thin film (x=0.20) fabricated using an alkoxide solution with partial hydrolysis, the grain and crystallite size were increased, and the er and d33 were improved to 253 and 8.9 pm/V, respectively.

Grain Size Effect on Dielectric and Piezoelectric Properties of Alkoxy-Derived BaTiO3-Based Thin Films

Lead- and bismuth-free Ba(Ti1-xZrx)O3 (BTZ) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by the chemical solution deposition (CSD) process. The BaTiO3 and BTZ005 thin films fabricated by the conventional process were observed to have a remarkable difference in grain size along the depth of the thin film. The microstructure of the BaTiO3 and BTZ005 thin films was improved by additional sintering process, and their grain sizes were increased to about 60 and 40 nm, respectively, by additional sintering at 800°C for 1 h. The dielectric constant er and piezoelectric constant d33 of the BaTiO3 thin film consisting of large grains by the additional sintering at 800°C for 1 h were found to be about 375 and 14.5 pm/V. But, er and d33 of the BTZ005 thin film changed negligibly with increasing of the grain size.

New material design with V1−xWxO2 film for sky radiator to obtain temperature stability

Spectral selective radiating material (SSRM ) such as a SiO film deposited on metallic substrate can be cooled lower than the ambient temperature due to its high IR emission in the spectral region of the atmospheric window under clear sky conditions. In this paper we propose a new stacked SSRM consisting of SiO film and V 1-x W x O 2 thermochromic film to stabilize the surface temperature of the sky radiator. The transition temperature from metallic to semiconductor phase of V 1-x W x O 2 thermochromic film can be adjusted to a temperature near ambient by the control of the doping level of x. The radiative cooling of the new SSRM was simulated using the optical constants of SiO and V 1-x W x O 2 obtained by optical measurements. The results reveal that the newly designed SSRM can attain a stable surface temperature determined by the transition temperature of the V 1-x W x O 2 film.

Optical properties of Pb doped TiO2 nanocrystalline thin films : A photoluminescence spectroscopic study

Abstract Pure and Pb doped TiO 2 semiconductor thin films are deposited on single crystal Si (100) surface by a simple sol-gel method with a Pb content of 5, 10 and 15 mol%, under different temperatures (550, 750 and 850°C). The crystal structure, surface morphology and optical properties of the films, deposited on a Si (100) surface, have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy, respectively. XRD patterns indicate the amorphous/nanocrystalline nature of the films together with the presence of pure anatase (A) to an anatase/rutile (A/R) mixture as the temperature increases from 550°C to 850°C. The surface morphology of the films reveal a porous structure with particle size in the range of 15 nm to 100 nm. An intense green photoluminescence is observed in the visible region for pure TiO 2 and the intensity gradually decreases by doping with lead, at all deposition (550, 750 and 850°C) and measuring (4.2, 77 and 300 K) temperatures.

Preparation of (Y,Yb)MnO3/Y2O3/Si (MFIS) Structure by Chemical Solution Deposition Method

(Y,Yb)MnO3 films were prepared on Y2O3-buffered n-type Si(111) substrates using alkoxy-derived precursor solutions and rapid thermal annealing at 750°C in Ar. The (Y,Yb)MnO3 films crystallized to hexagonal phase and had high crystallinity and high degrees of c-axis orientation. The hexagonal (Y,Yb)MnO3 films consisted of uniform grains and had smooth surfaces. The electrical properties of the 200-nm-thick Y0.5Yb0.5MnO3 films crystallized on the Y2O3/Si(111) substrates at 750°C in Ar were investigated. The leakage current density of the Pt/Y0.5Yb0.5MnO3/Y2O3/Si capacitor was 1.0×10-8 A/cm2 at an applied voltage of 5 V. The counterclockwise capacitance-voltage (C-V) hysteresis induced by ferroelectric polarization switching was observed in the Pt/Y0.5Yb0.5MnO3/Y2O3/Si capacitor.

Ferroelectric properties of alkoxy-derived CaBi2Ta2O9 thin films

CaBi2Ta2O9 thin films were deposited on Pt-passivated quartz glass substrates. The 750u200a°C-annealed thin film was a single phase of layer-structured perovskite and showed random orientation. The thin film exhibited a P–E hysteresis loop. The remanent polarization (Pr) and coercive electric field (Ec) at 13 V were 6 μC/cm2 and 160 kV/cm, respectively. The polarization did not show fatigue after 2×1010 switching cycles.

Thickness Dependence of Electrical Properties of Highly (100)-Oriented BaTiO3 Thin Films Prepared by One-Step Chemical Solution Deposition

Highly (100)-oriented BaTiO3 thin films having different thicknesses of 70–280 nm were deposited on Pt/TiOx/SiO2/Si substrates with LaNiO3 as a buffer layer by one-step chemical solution deposition. X-ray diffraction analyses showed that the LaNiO3 and BaTiO3 layers were all under tensile stress. The tensile stress of the LaNiO3 layer increased after depositing BaTiO3 films. The tensile stress in both the LaNiO3 and BaTiO3 layers decreased with increasing BaTiO3 layer thickness. The thickness dependences of the dielectric and piezoelectric behaviors of the highly (100)-oriented BaTiO3 films were investigated. It was found that the effect of tensile stress on the dielectric and piezoelectric properties is dominant. A reduction in in-plane tensile stress (primarily arising from a thermal expansion mismatch) was considered effective for increasing the dielectric and piezoelectric constants. The measured dielectric constant increased from about 313 for 70 nm films up to 831 for 280 nm films. The local effective piezoelectric coefficient increased from 15 pm/V for 70 nm films up to 45 pm/V for 280 nm films.